The availabilility of ion accelerators and storage rings have vastly
increased the ability to measure ionization cross sections (e.g.
Müller et
al. 1985,
Müller et
al. 1991).
But although there have been a much larger
number of experiments for ionization than for electron impact
excitation, most of the atomic systems, and their ions, have not yet
been measured. Much of the experimental work has been carried out at Oak
Ridge National Laboratory and the measured cross sections have been compiled
in a recent work ``Electron-Impact Ionization of Multicharged Ions at
ORNL: 1985-1992'' by D.C.Gregory and M.E. Bannister (1994, ORNL/TM-12729).
The experimental data have clearly established the importance of
excitation-autoionization (E-A) resonances that can enhance the cross section
by orders of magnitude above the background. Theoretical calculations
are now carried out for both the direct ionization and the E-A processes.
Recent work includes the important iron isonuclear sequence
(Pindzola et al. 1987),
used by
Arnaud and Raymond
(1992)
in their ionization balance
calculations for Iron. Following are general references to available
data (see also references in
Arnaud and
Rothenflug 1985).